Enzymatic production of (meth)acrylic esters that contain urethane groups

ABSTRACT

Enzymatic preparation of (meth)acrylic esters containing urethane groups, and their use in radiation-curable compositions.

DESCRIPTION

The present invention relates to a process for preparing (meth)acrylicesters containing urethane groups and to the use thereof inradiation-curable coating compositions.

(Meth)acrylic esters are generally prepared by acid- or base-catalyzedesterification or transesterification of (meth)acrylic acid or other(meth)acrylic esters with alcohols at temperatures from 40 to well above100° C. In view of the high temperatures it is necessary to add largeamounts of polymerization inhibitors in order to suppress any unwantedpolymerization of the monomers. This often produces complex andoccasionally colored product mixtures. In order to remove colorationsand unreacted reactants the product mixtures are worked up by expensivealkaline washes. The washing process is lengthy and costly, sincepartially esterified products in particular are slow to extract andseparate.

The preparation of (meth)acrylates containing urethane groups byconventional acid-catalyzed esterification, moreover, is difficult,because urethane groups are acid sensitive.

JP-A 2001-40039 describes (meth)acrylic esters that contain carbamategroups and are prepared by way of an acid-catalyzed esterification.

A disadvantage of the process described is that the purity of theresultant product is only 75.9% for a mass balance of 95%.

EP-A1 36 813 describes the two-stage preparation of N-substitutedacrylates containing carbamate groups by reacting multiplyhydroxyalkylated acrylates with isocyanates.

A disadvantage of the process described is the restriction to thosesubstrates which are available in the form of isocyanates. For example,N,N-disubstituted carbamates cannot be prepared by this process, and norcan those with nitrogen substituents which carry isocyanate-reactivegroups. For reaction with the isocyanate, moreover, toxic tin compoundcatalysts are required.

The preparation of (meth)acrylic esters by an enzymatic esterificationor transesterification is known.

Hajjar et al. in Biotechnol. Lett. 1990, 12, 825–830 describe theenzymatic transesterification of cyclic and open-chain alkanediols withethyl acrylate using a lipase from Chromobacterium viscosum. Thereactions proceed with an 18-fold molar excess of the alkyl acrylateover the diol in a solvent-free system. This produces mixtures ofmonoacrylates and diacrylates.

U.S. Pat. No. 5,240,835 describes the transesterification of alkylacrylates with alcohols with catalysis by a biocatalyst fromCorynebacterium oxydans. Depicted by way of example therein is thereaction of a 96-fold molar excess of ethyl acrylate with2,2-dimethyl-1,3-propanediol. A yield of only 21% was obtained after 3days at 30° C.

Derango et al. in Biotechnol. Lett. 1994, 16, 241–246 describe thelipase-catalyzed preparation of carbamoyloxyethyl methacrylate bytransesterification of 2-hydroxyethyl carbamate with vinyl methacrylate.Complete reaction is achieved by the specific vinyl methacrylatereactant, since vinyl alcohol liberated is removed from the reactionequilibrium in the form of acetaldehyde. A disadvantage of this processis that vinyl methacrylate is not commercially available.

The use of (meth)acrylic esters containing urethane groups inradiation-curable coating compositions is known from EP-A1 263 749.

It is an object of the present invention to provide a process by which(meth)acrylic esters containing urethane groups can be prepared in highconversions and high purities from simple reactants which are classed asless toxicologically objectionable than vinyl methacrylate. Thesynthesis ought to run under mild conditions, to give products having alow color number and viscosity.

We have found that this object is achieved by a process for preparing(meth)acrylic esters (F) containing urethane groups by

-   c) reacting an alcohol (C) containing urethane groups with    (meth)acrylic acid or with an ester of (meth)acrylic acid with a    saturated alcohol (D), and-   d) if desired, working up the reaction mixture from c), the    reaction c) being conducted in the presence of an enzyme (E).

The process of the invention allows (meth)acrylic esters containingurethane groups to be prepared in high chemical and space/time yield andunder mild conditions. With the process of the invention it is possible,advantageously, to prepare (meth)acrylic esters, containing urethanegroups, that have less coloration and/or lower viscosity than inaccordance with the prior art. As a further advantage it is possible toreduce the use of polymerization inhibitors, and with particularadvantage they can be dispensed with entirely.

Urethane groups for the purposes of this document are O-substituted andN-unsubstituted, monosubstituted or disubstituted structural elements ofthe formula >N—C(═O)—O—.

(Meth)acrylic acid in this document stands for methacrylic acid andacrylic acid, preferably for acrylic acid.

Alcohols (C) containing urethane groups are compounds which comprise atleast one urethane group, preferably from 1 to 10, more preferably from1 to 5, very preferably 1 or 2, and in particular one urethane group,and also at least one hydroxyl group (—OH), preferably from 1 to 10,more preferably from 1 to 6, very preferably from 1 to 3, in particular1 or 2, and especially one hydroxyl group.

Preferred alcohols (C) containing urethane groups have an average molarweight of from 105 to 800 000 g/mol, preferably from 120 to 25 000, morepreferably from 200 to 5000, and very preferably from 400 to 4500 g/mol.

Particularly preferred alcohols (C) containing urethane groups are thoseobtainable by

-   a) reacting an amine (A) with a carbonate (B), and-   b) if desired, working up the reaction mixture obtainable from a).

Amines in this case are ammonia, primary or secondary amines, andcarbonates are O,O′-di-substituted carbonates having the structuralelement —O—C(═O)—O—.

Especially preferred alcohols (C) containing urethane groups are thoseobtainable by a reaction as per formula I

in which

-   R³, R⁴ independently are hydrogen, C₁–C₁₈ alkyl, C₂–C₁₈ alkyl    uninterrupted or interrupted by one or more oxygen and/or sulfur    atoms and/or by one or more substituted or unsubstituted imino    groups, or are C₂–C₁₈ alkenyl, C₆–C₁₂ aryl, C₅–C₁₂ cycloalkyl or a    five- to six-membered heterocycle containing oxygen, nitrogen and/or    sulfur atoms, it being possible for each of the radicals stated to    be substituted by aryl, alkyl, aryloxy, alkyloxy, heteroatoms and/or    heterocycles, or are a group of the formula —[X_(i)]_(k)—H,-   Y is C₂–C₂₀ alkylene or C₅–C₁₂ cycloalkylene or is C₂–C₂₀ alkylene    which is interrupted by one or more oxygen and/or sulfur atoms    and/or by one or more substituted or unsubstituted imino groups    and/or by one or more cycloalkyl, —(CO)—, —O(CO)O—, —(NH)(CO)O—,    —O(CO)(NH)—, —O(CO)— or —(CO)O— groups, it being possible for each    of the radicals stated to be substituted by aryl, alkyl, aryloxy,    alkyloxy, heteroatoms and/or heterocycles,-   k is a number from 1 to 50, and-   X_(i) for i=1 to k can be selected independently from the group    consisting of —CH₂—CH₂—O—, —CH₂—CH₂—N(H)—, —CH₂—CH₂—CH₂—N(H)—,    —CH₂—CH(NH₂)—, —CH₂—CH(NHCHO)—, —CH₂—CH(CH₃)—O—, —CH(CH₃)—CH₂—O—,    —CH₂—C(CH₃)₂—O—, —C(CH₃)₂—CH₂—O—, —CH₂—CH₂—CH₂—O—,    —CH₂—CH₂—CH₂—CH₂—O—, —CH₂—CHVin-O—, —CHVin-CH₂—O—, —CH₂—CHPh—O—, and    —CHPh—CH₂—O—, where Ph stands for phenyl and Vin stands for vinyl.-   R³ and R⁴ can also together form a ring.

Preferably R³ and R⁴ independently are hydrogen, C₁–C₁₂ alkyl, C₅–C₆cycloalkyl or a group of the formula —[X_(i)]_(k)—H; with particularpreference R³ and R⁴ independently are hydrogen, C₁–C₄ alkyl, C₅–C₆cycloalkyl or a group of the formula —[X_(i)]_(k)—H; and very preferablyR³ and R⁴ are hydrogen, C₁–C₄ alkyl, or a group of the formula—[X_(i)]_(k)—H. In particular, one of the radicals R³ and R⁴ is hydrogenand the other is C₁–C₄ alkyl, or a group of the formula —[X_(i)]_(k)—H.

Y is preferably C₂–C₁₀ alkylene, more preferably C₂–C₆ alkylene, verypreferably C₂–C₄ alkylene, in particular C₂–C₃ alkylene, and especiallyC₂ alkylene, it being possible for each of the radicals stated to besubstituted by aryl, alkyl, aryloxy, alkyloxy, heteroatoms and/orheterocycles.

k is preferably 1 to 30, more preferably 1 to 20, very preferably 1 to10, and in particular 1 to 5.

Preferred X₁ are —CH₂—CH₂—O—, —CH₂—CH₂—N(H)—, —CH₂—CH₂—CH₂—N(H)—,—CH₂—CH(NH₂)—, —CH₂—CH(NHCHO)—, —CH₂—CH(CH₃)—O— and —CH(CH₃)—CH₂—O—,more preferably —CH₂—CH₂—O—, —CH₂—CH₂—N(H)—, —CH₂—CH₂—CH₂—N(H)— and—CH₂—CH(NH₂)—, very preferably —CH₂—CH₂—O—, —CH₂—CH₂—N(H)—, and—CH₂—CH₂—CH₂—N(H)—.

Examples of R³ and/or R⁴ are hydrogen, methyl, ethyl, isopropyl,n-propyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-hexyl, n-heptyl,n-octyl, n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl, n-octadecyl,n-eicosyl, 2-ethylhexyl, cyclopentyl, cyclohexyl, cyclooctyl,cyclododecyl, 2-hydroxyethyl, 2-hydroxypropyl, 1-hydroxypropyl,5-hydroxy-3-oxapentyl, 8-hydroxy-3,6-dioxaoctyl or11-hydroxy-3,6,9-trioxaundecyl.

Examples of Y are 1,2-ethylene, 1,2-propylene,1,1-dimethyl-1,2-ethylene, 1-hydroxymethyl-1,2-ethylene,2-hydroxy-1,3-propylene, 1,3-propylene, 1,4-butylene, 1,6-hexylene,2-methyl-1,3-propylene, 2-ethyl-1,3-propylene,2,2-dimethyl-1,3-propylene, and 2,2-dimethyl-1,4-butylene, preferably1,2-ethylene, 1,2-propylene, and 1,3-propylene, more preferably1,2-ethylene and 1,2-propylene, and very preferably 1,2-ethylene.

Exemplary amines (A) are ammonia, methylamine, dimethylamine,ethylamine, diethylamine, isopropylamine, diisopropylamine,n-butylamine, di-n-butylamine, tert-butylamine, monoethanolamine,diethanolamine, propanolamine, dipropanolamine, piperidine, piperazine,pyrrolidine, cyclopentylamine, cyclohexylamine, aniline,ethylenediamine, diethylenetriamine, triethylenetetramine,tetraethylenepentamine, and polyethyleneimines having a weight-averagemolecular weight M_(w) of from 200 to 25 000 g/mol, preferably from 400to 8000, more preferably from 750 to 5000, and very preferably from 800to 3000 g/mol. Polyethyleneimines which can be used in accordance withthe invention have a ratio of primary:secondary:tertiary amine groups offor example 1:0.75–1.25:0.4–0.8. It is of course also possible to usepolyethyleneimines with a higher molecular weight, going for example upto a molecular weight M_(w) of 2 000 000, preferably up to 750 000;since, however, such polyethyleneimines are usually present in aqueoussolution, the solvent should be removed and/or replaced by another priorto their use in the reaction according to the invention.

Examples of further possible amines (A) include hydrogenatedpolyacrylonitriles, straight-chain, branched or dendritic polymerscontaining amino functions, or at least partly hydrolyzedpoly-N-vinylformamides.

Examples of straight-chain polymers containing amino functions arepolyethylene glycols, polypropylene glycols, mixed polyalkylene oxides,poly-1,3-propanediols, poly-THF or alkoxylated polyols or monools inwhich at least one terminal hydroxyl group has been replaced by an aminogroup, and also amino-functionalized polyisobutenes, in each case with aweight-average molecular weight M_(w) from 200 to 25 000 g/mol,preferably from 400 to 8000, more preferably from 750 to 5000, and verypreferably from 800 to 3000 g/mol. Examples thereof are Jeffamines® fromHuntsman Corp., Houston.

Branched polymers containing amino functions are for example describedin WO 93/14147, p. 2, line 3–p. 6, line 14, whose preparation isdescribed in the same document and also in WO 95/02008 and WO 97/23514,or those branched polymers whose preparation is described in WO95/20619, and also the polyethylene glycol-polyethyleneimine blockpolymers described in Biomacromolecules, 2002, 3, 926–936.

Preferred branched polymers are, for example, the dendrimers preparedstarting from 1,4-diaminobutane and obtainable by alternating Michaeladdition of acrylonitrile and hydrogenation of the nitrile group,including those of the 1st generation (Astramol® Am-4, from DSM, TheNetherlands, CAS No. [120239-63-6]), of the 2nd generation (Astramol®Am-8, from DSM, The Netherlands, CAS No. [154487-83-9]), of the 3rdgeneration (Astramol® Am-16, CAS No. [154487-85-1]), of the 4thgeneration (Astramol® Am-32, CAS No. [163611-04-9]) or of the 5thgeneration (Astramol® Am-64, CAS No. [163611-05-0]).

At least partly hydrolyzed poly-N-vinylformamides are for exampledescribed in EP B1 71 050, p. 1, line 31 to p. 4, line 54. Preferredhydrolyzed poly-N-vinylformamides are those having a K value (inaccordance with Fikentscher, measured in 0.5% strength by weight aqueoussodium chloride solution at 25° C.) of between 10 and 110, with K valuesbetween 30 and 80 being particularly preferred, and having a degree ofcleavage (degree of hydrolysis of the formyl group) of from 10 to 100mol %, more preferably from 10 to 80, very preferably from 20 to 60, andwith especial preference from 30 to 50 mol %.

Exemplary carbonates (B) are ethylene carbonate, 1,3-propylenecarbonate, and 1,2-propylene carbonate.

The reaction of an amine (A) with a carbonate (B) is known per se, fromU.S. Pat. No. 4,820,830, col. 4, line 44 to col. 5, line 9, for example,and is not restricted.

Typically the amine (A) and the carbonate (B) are reacted with oneanother in a stoichiometry of from 0.7 to 1.2 mol of amine: 1 mol ofcarbonate, preferably 0.8–1.2:1, more preferably 0.9–1.1:1, verypreferably 0.95–1.1:1, and especially 1:1 mol/mol. The reaction takesplace in general at a temperature of from 0 to 120° C., in particularfrom 20 to 100° C., more preferably from 30 to 80° C., and verypreferably from 40 to 80° C. The reaction is generally over within 12hours, preferably within from 15 minutes to 10 hours, more preferably infrom 30 minutes to 8 hours, very preferably from 45 minutes to 6 hours,and in particular within 1 to 4 hours.

The total amine number to DIN 53176 of the reaction product shouldamount to not more than 200 mg KOH/g, preferably to not more than 100,and very preferably to not more than 80 mg KOH/g.

The reaction can be carried out without a solvent or in the presence ofone, examples being alcohols, ethers, ketones, hydrocarbons, and water,but preferably without solvent.

The reaction mixture obtainable from a) can be worked up if desired in afurther step b), by for example filtration, distillation, rectification,chromatography, treatment with ion exchangers, treatment withadsorbents, neutral, acidic and/or alkaline washing, stripping orcrystallization.

One preferred embodiment of the present invention is constituted by(meth)acrylic esters containing urethane groups and obtainable by

-   a) reacting a polyethyleneimine, a hydrogenated polyacrylonitrile, a    branched polymer having amino functions or an at least partly    hydrolyzed poly-N-vinylformamide having a weight-average molecular    weight M_(w) of from 200 to 1 000 000, preferably 200–750 000, more    preferably 200–25 000, very preferably 400–8000, in particular    750–5000, and especially 800–3000 g/mol with a carbonate (B) at a    temperature of from 0 to 120° C.,-   b) if desired, working up the reaction mixture obtainable from a),-   c) reacting the reaction mixture from a) or b) with (meth)acrylic    acid or with an ester of (meth)acrylic acid with a saturated    alcohol (D) in the presence of an enzyme (E), and-   d) if desired, working up the reaction mixture from c).

Preference is given to reacting linear or branched polyethyleneimines,dendrimers containing amino functions, or at least partly hydrolyzedpoly-N-vinylformamides, more preferably polyethyleneimines or dendrimerscontaining amino functions, and very preferably polyethyleneimines.

In step c) the alcohol containing urethane groups is transesterified oresterified with at least one (meth)acrylate or (meth)acrylic acid (D) inthe presence of an enzyme (E) which catalyzes the (trans)esterification.

Compounds (D) can be (meth)acrylic acid or esters of (meth)acrylic acidwith a saturated alcohol, preferably (meth)acrylic acid and thesaturated C₁–C₁₀ alkyl esters thereof.

Saturated compounds for the purposes of this text are compounds withoutC—C multiple bonds (except of course for the C═C double bond in the(meth)acrylic units).

Examples of compounds (D) are (meth)acrylic acid and methyl, ethyl,n-butyl, isobutyl, n-octyl, and 2-ethylhexyl (meth)acrylate,1,2-ethylene glycol di(meth)acrylate and mono(meth)acrylate,1,4-butanediol di(meth)acrylate and mono(meth)acrylate, 1,6-hexanedioldi(meth)acrylate and mono(meth)acrylate, trimethylolpropanetri(meth)acrylate, and pentaerythritol tetra(meth)acrylate.

Particular preference is given to (meth)acrylic acid and to methyl,ethyl, n-butyl, and 2-ethylhexyl (meth)acrylate, and very particularpreference to methyl, ethyl, and n-butyl (meth)acrylate.

The enzymatic (trans)esterification with a (meth)acrylate or(meth)acrylic acid takes place in general at from 0 to 100° C.,preferably from 20 to 80° C., more preferably from 20 to 70° C., andvery preferably from 20 to 60° C.

Enzymes (E) which can be used in accordance with the invention areselected for example from hydrolases, esterases (E.C. 3.1.-.-), lipases(E.C. 3.1.1.3), glycosylases (E.C. 3.2.-.-) and proteases (E.C. 3.4.-.-)in free form or in a form in which they are chemically or physicallyimmobilized on a carrier, preferably lipases, esterases or proteases.Particular preference is given to Novozyme 435 (lipase from Candidaantarctica B) or lipase from Aspergillus sp., Aspergillus niger sp.,Mucor sp., Penicillium cyclopium sp., Geotricum candidum sp., Rhizopusjavanicus, Burkholderia sp., Candida sp., Pseudomonas sp., or porcinepancreas, very particular preference to lipase from Candida antarctica Bor from Burkholderia sp.

The enzyme content of the reaction medium lies generally in the rangefrom about 0.1 to 10% by weight, based on the sum of the components (C)and (D) employed. The reaction time depends among other things on thetemperature, on the amounts and activity of the enzyme catalyst used,and on the required conversion, and also on the alcohol containingurethane groups. The reaction time is preferably adapted so that theconversion of all hydroxyl functions originally present in the alcohol(C) is at least 70%, preferably at least 80%, more preferably at least90% and very preferably at least 95%. For this a time of from 1 to 48hours and preferably from 1 to 12 hours is generally sufficient.

The molar ratio of (meth)acrylic acid compound (D) (based on the(meth)acrylic units) to alcohol (C) containing urethane groups (based onhydroxyl groups) can vary within a wide range, such as in a ratio offrom 100:1 to 1:1, preferably from 50:1 to 1:1, more preferably from20:1 to 1:1, and very preferably from 10:1 to 1:1.

The reaction can proceed in organic solvents or mixtures thereof orwithout the addition of solvents. The reaction mixtures are generallysubstantially anhydrous (i.e., with addition of less than 10%,preferably less than 5%, by volume of water).

The fraction of organic solvents is for example 0.01–90% by weight.Suitable organic solvents are those known for these purposes, examplesbeing tertiary monools, such as C₃–C₆ alcohols, preferably tert-butanolor tert-amyl alcohol, pyridine, poly-C₁–C₄ alkylene glycoldi-C₁–C₄-alkyl ethers, preferably polyethylene glycol di-C₁–C₄ alkylethers, such as 1,2-dimethoxyethane, diethylene glycol dimethyl ether,polyethylene glycol dimethyl ether 500, for example, C₁–C₄ alkylenecarbonates, especially propylene carbonate, C₃–C₆ alkyl acetic esters,especially tert-butyl acetate, THF, toluene, 1,3-dioxolane, acetone,isobutyl methyl ketone, ethyl methyl ketone, 1,4-dioxane, tert-butylmethyl ether, cyclohexane, methylcyclohexane, toluene, hexane,dimethoxymethane, 1,1-dimethoxyethane, acetonitrile, and thesingle-phase or multiphase mixtures thereof. It can be advantageous toseparate off water of reaction by means of a binary or ternaryheteroazeotrope which boils as close as possible to the temperatureoptimum of the enzyme used, an example being ethyl methylketone/hexane/water. The water removed azeotropically can then beremoved by phase separation or membrane vapor separation.

An option is to add aqueous solvents to the organic solvents, to producereaction solutions which depending on the organic solvent take the formof a single phase or multiple phases. Examples of aqueous solvents arewater and also aqueous dilute (e.g., 10 to 100 mM) buffers, with a pHfor example in the range from about 6 to 8, such as potassium phosphatebuffer or TRIS HCl buffer, for example.

The water fraction in the reaction mixture is generally 0–10% by volume.Preferably the reactants are used without pretreatment (drying, waterdoping).

The substrates are alternatively in solution, in suspension as solids,or in emulsion in the reaction medium. The initial concentration of thereactants is preferably in the range from about 0.1 to 20 mol/l, inparticular from 0.15 to 10 mol/l or from 0.2 to 5 mol/l.

The reaction can take place continuously, in a tube reactor or in acascade of stirred reactors, for example, or batchwise.

The reaction can be carried out in all reactors that are suitable forsuch reaction. Reactors of this kind are known to the skilled worker.The reaction takes place preferably in a stirred tank reactor or in afixed bed reactor.

The reaction mixture can be mixed by a variety of methods. There is noneed for special stirring equipment. The reaction medium can be singlephase or have a plurality of phases and the reactants are dissolved,suspended or emulsified therein, introduced into the reaction vesseltogether where appropriate with the molecular sieve, and admixed withthe enzyme preparation at the beginning of the reaction and also, whereappropriate, one or more times during the course of the reaction. Duringthe reaction the temperature is set at the desired level and can beraised or lowered if desired during the course of the reaction.

If the reaction is carried out in a fixed bed reactor the reactor ispreferably packed with immobilized enzymes, with the reaction mixturebeing pumped through a column packed with the enzyme. It is alsopossible to carry out the reaction in a fluidized bed, with the enzymebeing used in immobilized form on a carrier. The reaction mixture can bepumped continuously through the column, in which case the residence timeand hence the desired conversion can be controlled via the flow rate.Another possibility is to pump the reaction mixture through a column incirculation, in which case it is possible at the same time to remove thewater of reaction and/or the liberated alcohol by distillation, underreduced pressure where appropriate.

The removal of the water of reaction or of alcohols which are liberatedfrom the alkyl acrylates in the case of a transesterification takesplace continuously or gradually in a manner known per se, for example byreduced pressure, azeotropic removal, absorption, pervaporation, anddiffusion via membranes.

Means suitable for this purpose include preferably molecular sieves(pore size in the region of about 3–10 Angströms, for example),separation by distillation, or separation with the aid of suitablesemipermeable membranes.

After the end of the reaction the reaction mixture obtainable from c)can be used further without additional workup or if required can beworked up in a further step d).

d) In general only the enzyme used and any molecular sieve used areseparated from the reaction mixture and the reaction product isseparated from any organic solvent used.

Enzyme is generally separated off by filtration, absorption,centrifugation or decanting. The enzyme separated off can then beemployed for further reactions.

Separation from organic solvent takes place in general by distillation,by rectification or, in the case of solid reaction products, byfiltration.

For further workup of the reaction product it is also possible to carryout chromatography.

Preferably in step d), however, only the enzyme used and any solventused are separated off.

The reaction conditions for the enzymatic esterification ortransesterification are mild. The low temperatures and other mildconditions prevent the formation in step c) of byproducts which mightotherwise originate, for example, from chemical catalysts or as a resultof unwanted free-radical polymerization of the (meth)acrylate or(meth)acrylic acid used, which can otherwise be prevented only by addingstabilizers. In the reaction regime according to the invention it ispossible to add stabilizer to the (meth)acrylic compound (D) above andbeyond the storage stabilizer which is present in any case, examples ofsuch additional stabilizers being hydroquinone monomethyl ether,phenothiazine, phenols, such as 2-tert-butyl-4-methylphenol or6-tert-butyl-2,4-dimethylphenol, or N-oxyls, such as4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl or4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl, in amounts of from 50 to2000 ppm, for example. The (trans)esterification is conductedadvantageously in the presence of an oxygen-containing gas, preferablyair or air/nitrogen mixtures. In addition there is no difficulty inseparating the enzyme catalyst from the end product. Moreover, generallyspeaking, there is no substantial discernible cleavage of the urethanegroups as a result of enzymatic hydrolysis: the level of byproducts isgenerally less than 10%, preferably less than 5%.

By the process of the invention it is possible in one particularlypreferred embodiment to obtain (meth)acrylic esters (F) containingurethane groups, of the formula (II)

in which

-   R³ and R⁴ are as defined above,-   Y is selected from 1,2-ethylene, 1,2-propylene,    1,1-dimethyl-1,2-ethylene, 1-hydroxymethyl-1,2-ethylene,    2-hydroxy-1,3-propylene, 2-hydroxy-1,3-propylene, 1,3-propylene,    1,4-butylene, 1,6-hexylene, 2-methyl-1,3-propylene,    2-ethyl-1,3-propylene, 2,2-dimethyl-1,3-propylene, and    2,2-dimethyl-1,4-butylene, or

or 1,2-, 1,3- or 1,4-cyclohexylene,

-   R¹ is hydrogen or methyl, preferably hydrogen, with the proviso that    at least one of the radicals R³ and R⁴ is other than hydrogen.

In radiation-curable coating compositions these (meth)acrylic esterscontaining urethane groups effect a sharp increase in the scratchresistance and elasticity while being of low viscosity, thereby makingthe compounds of the formula (II) valuable constituents ofradiation-curable coating compositions.

An advantage of the process of the invention is that substantiallycomplete conversions can be achieved with simple (meth)acrylic compounds(D) on account of the fact that the reaction equilibrium can be shiftedwithout the need to use specialty reactants such as vinyl methacrylatefor example.

The (meth)acrylic esters containing urethane groups that are obtainablefrom stages c) and d) respectively can be used with advantage ascomonomers in, for example, poly(meth)acrylates or as reactive diluentsin radiation-curable and/or dual cure poly(meth)acrylates.Poly(meth)acrylates of this kind are suitable for use as binders inradiation-curable or dual cure coating materials.

Coatings obtainable in this way feature very high scratch resistance,hardness, chemical resistance, elasticity, and adhesion, on bothhydrophilic and hydrophobic substrates.

The (meth)acrylic esters containing urethane groups that are prepared inaccordance with the invention can also be used advantageously, onaccount of their relatively low coloration, in a thermally induced(free-radical) (co)polymerization.

Examples of monomers with which the urethane-group-containing(meth)acrylic esters prepared in accordance with the invention can becopolymerized by way of example include C₁–C₂₀ alkyl (meth)acrylates,vinylaromatics having up to 20 carbon atoms, vinyl esters of carboxylicacids comprising up to 20 carbon atoms, ethylenically unsaturatednitrites, vinyl ethers of alcohols comprising 1 to 10 carbon atoms, andaliphatic hydrocarbons having 2 to 8 carbon atoms and 1 or 2 doublebonds.

The term (meth)acrylic acid is used within this specification foracrylic acid and methacrylic acid.

Preferred alkyl (meth)acrylates are those with a C₁–C₁₀ alkyl radical,such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethylacrylate, and branched alkyl derivatives such as 2-ethylhexyl acrylate.

Mixtures of the alkyl (meth)acrylates in particular are also suitable.

Vinyl esters of carboxylic acids having 1 to 20 carbon atoms are, forexample, vinyl laurate, vinyl stearate, vinyl propionate, and vinylacetate.

Examples of suitable vinylaromatic compounds include vinyltoluene,α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, and styrene, thelatter being preferred.

Examples of nitriles are acrylonitrile and methacrylonitrile.

Suitable vinyl ethers include for example vinyl methyl ether, vinylisobutyl ether, vinyl hexyl ether, and vinyl octyl ether.

Nonaromatic hydrocarbons having 2 to 8 carbons and one or two olefinicdouble bonds include butadiene, isoprene, and also ethylene, propylene,and isobutylene.

A frequent, though not the only, method of preparing such (co)polymersis that of free-radical or ionic (co)polymerization in a solvent ordiluent.

The free-radical (co)polymerization of such monomers takes place forexample in aqueous solution in the presence of polymerization initiatorswhich under polymerization conditions disintegrate into free radicals,examples being peroxodisulfates, H₂O₂ redox systems or hydroxyperoxides, such as tert-butyl hydroperoxide or cumene hydroperoxide, forexample. The (co)polymerization may be performed within a widetemperature range, if appropriate under reduced pressure or else underelevated pressure, in general at temperatures up to 100° C. The pH ofthe reaction mixture is commonly set in the range from 4 to 10.

The (co)polymerization can, however, also be carried out in a differentway, known per se to the skilled worker, continuously or batchwise, inthe form, for example, of a solution, precipitation, water-in-oilemulsion, inverse emulsion, suspension or inverted suspensionpolymerization.

In this case the monomer/the monomers is or are (co)polymerized usingfree-radical polymerization initiators, examples being azo compoundswhich disintegrate into free radicals, such as2,2′-azobis(isobutyronitrile),2,2′-azobis(2-amidinopropane)hydrochloride or4,4′-azo-bis(4′-cyanopentanoic acid) or dialkyl peroxides, such asdi-tert-amyl peroxide, aryl alkyl peroxides, such as tert-butyl cumylperoxide, alkyl acyl peroxides, such as tert-butylperoxy-2-ethylhexanoate, peroxydicarbonates, such asdi(4-tert-butylcyclohexyl)peroxydicarbonate, or hydroperoxides.

The stated compounds are used mostly in the form of aqueous solutions oraqueous emulsions, the lower concentration being determined by theamount of water that is acceptable in the (co)polymerization, and theupper concentration by the solubility of the respective compound inwater.

Examples of solvents or diluents which can be used include water,alcohols, such as methanol, ethanol, n- or isopropanol, n- orisobutanol, or ketones, such as acetone, ethyl methyl ketone, diethylketone or isobutyl methyl ketone. Particular preference is given to apolar solvents such as, for example, xylene and its isomer mixtures, andto Shellsol® A and solvent naphtha.

In one preferred embodiment the monomers are premixed and initiator isadded with further additions, if appropriate, in solution in solvent.One particularly preferred embodiment is described in WO 01/23484 onpage 10, line 3 to line 24 therein in particular.

If appropriate the (co)polymerization can be carried out in the presenceof polymerization regulators, such as hydroxylammonium salts,chlorinated hydrocarbons and thio compounds, for example, such astert-butyl mercaptan, thioglycolic acid ethylacrylic ester,mercaptoethynol, mercaptopropyltrimethoxysilane, dodecyl mercaptan,tert-dodecyl mercaptan or alkali metal hypophosphites. In the case ofthe (co)polymerization it is possible for these regulators to be used inamounts, for example, of 0 to 0.8 parts by weight, based on 100 parts byweight of the monomers to be (co)polymerized, and they reduce the molarmass of the (co)polymer which forms.

In the course of the emulsion polymerization it is possible to usedispersants, ionic and/or nonionic emulsifiers and/or protectivecolloids, or stabilizers, as surface-active compounds. Suitable suchcompounds include both the protective colloids that are commonly usedfor carrying out emulsion polymerizations, and emulsifiers.

Examples of suitable protective colloids include polyvinyl alcohols,cellulose derivatives or vinyl-pyrrolidone copolymers. A detaileddescription of further suitable protective colloids is found inHouben-Weyl, Methoden der organischen Chemie, volume XIV/1,Makromolekulare Stoffe [Macromolecular compounds], Georg-Thieme-Verlag,Stuttgart, 1969, pp. 411 to 420. It is of course also possible to usemixtures of emulsifiers and/or protective colloids. As dispersants it ispreferred to use exclusively emulsifiers, whose relative molecularweights, unlike those of the protective colloids, are usually below1000. They may be anionic, cationic or nonionic in nature. Wheremixtures of surface-active substances are used it is of course necessaryfor the individual components to be compatible with one another,something which in case of doubt can be checked by means of a fewpreliminary tests. Generally speaking, anionic emulsifiers arecompatible with one another and with nonionic emulsifiers.

The same also applies to cationic emulsifiers, whereas anionic andcationic emulsifiers are mostly incompatible with one another. Examplesof customary emulsifiers include ethoxylated mono-, di- andtri-alkylphenols (EO degree: 3 to 100,: C₄ to C₁₂), ethoxylated fattyalcohols (EO degree: 3 to 100, alkyl radical: C₈ to C₁₈), and alsoalkali metal salts and ammonium salts of alkyl sulfates (alkyl radical:C₈ to C₁₆), of sulfuric monoesters with ethoxylated alkylphenols (EOdegree: 3 to 100, alkyl radical: C₄ to C₁₂), of alkylsulfonic acids(alkyl radical: C₁₂ to C₁₈) and of alkylarylsulfonic acids (alkylradical: C₉ to C₁₈). Further suitable emulsifiers such as sulfosuccinicesters are found in Houben-Weyl, Methoden der organischen Chemie, volumeXIV/1, Makromolekulare Stoffe, Georg-Thieme-Verlag, Stuttgart, 1961,pages 192 to 208.

In general the amount of dispersant used is 0.5 to 6%, preferably 1 to3%, by weight based on the monomers for free-radical polymerization.

Examples of (meth)acrylate-containing dispersions are n-butylacrylate/acrylonitrile dispersions, which are employed as adhesives,n-butyl acrylate/butadiene/styrene

The polymer dispersions in which (meth)acrylic esters containingurethane groups and prepared in accordance with the invention are usedmay additionally be chemically and/or physically deodorized.

The copolymers obtainable with the (meth)acrylic esters containingurethane groups and prepared in accordance with the invention generallyhave a relatively low color number, which is advantageous in thecoatings field. The copolymers described can then be reacted in a mannerknown per se with, for example, amino resins, such as melamine, forexample, to form crosslinked film-forming resins, as is described, forexample, in EP 738740 or EP 675141.

The present invention further provides accordingly for the use of the(meth)acrylic esters containing urethane groups prepared by the processof the invention as reactive diluents or binders in radiation-curable ordual cure coating compositions, preferably in top coats, more preferablyin transparent clearcoat materials. Of course the (meth)acrylic esterscontaining urethane groups prepared in accordance with the invention canalso be used as monomers in polymerizations, together where appropriatewith other polymerizable monomers, such as (meth)acrylic acid,(meth)acrylic esters, styrene, butadiene, acrylonitrile, vinyl acetate,N-vinylpyrrolidone, 4-hydroxybutyl vinyl ether or N-vinylformamide, forexample.

By dual cure is meant that the coating compositions are curablethermally and with actinic radiation. Actinic radiation for the purposesof the present invention is electromagnetic radiation such as visiblelight, UV radiation or X-rays, especially UV radiation, and corpuscularradiation such as electron beams.

Radiation-curable binders are those curable by means of actinicradiation as defined above, particularly by means of UV radiation.

The present invention further provides coating formulations comprisingthe (meth)acrylic esters containing urethane groups that are obtainableby the process of the invention. These esters can be used in bothbasecoat and topcoat materials. Because of their particular properties,such as that of increasing the scratch resistance and elasticity, and ofreducing the viscosity, particularly in the case of branchedpolyacrylates, of a radiation-cured clearcoat, their use in topcoats ispreferred.

Besides the (meth)acrylic esters (F) containing urethane groups that areobtainable by the process of the invention, a radiation-curablecomposition of the invention may include the following additionalcomponents:

-   (G) at least one polymerizable compound containing two or more    copolymerizable, ethylenically unsaturated groups,-   (H) if desired, reactive diluents,-   (I) if desired, photoinitiator, and-   (J) if desired, further typical coatings additives.

Suitable compounds (G) include radiation-curable, free-radicallypolymerizable compounds containing two or more copolymerizable,ethylenically unsaturated groups.

Compounds (G) are preferably vinyl ether compounds or (meth)acrylatecompounds, particular preference being given in each case to theacrylate compounds, i.e., the derivatives of acrylic acid.

Preferred vinyl ether compounds and (meth)acrylate compounds (G) containfrom 2 to 20, more preferably from 2 to 10, and very preferably from 2to 6 copolymerizable, ethylenically unsaturated double bonds.

Particularly preferred compounds (G) are those having an ethylenicallyunsaturated double bond content of 0.1–0.7 mol/100 g, very preferably0.2–0.6 mol/100 g.

The number-average molecular weight M_(n) of the compounds (G) unlessotherwise stated is preferably below 15 000, more preferably 300–12 000,very preferably from 400 to 5000, and in particular 500–3000 g/mol (asdetermined by gel permeation chromatography using polystyrene standardsand tetrahydrofuran eluent).

(Meth)acrylate compounds include (meth)acrylic esters and especiallyacrylic esters and also vinyl ethers of polyfunctional alcohols,particularly those which apart from the hydroxyl groups contain no otherfunctional groups or, if any at all, then ether groups. Examples of suchalcohols include difunctional alcohols, such as ethylene glycol,propylene glycol, and their more highly condensed counterparts, such asdiethylene glycol, triethylene glycol, dipropylene glycol, tripropyleneglycol etc., 1,2-, 1,3-, or 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol, alkoxylatedphenolic compounds, such as ethoxylated and/or propoxylated bisphenols,1,2-, 1,3-, or 1,4-cyclohexanedimethanol, alcohols with a functionalityof 3 or more, such as glycerol, trimethylolpropane, butanetriol,trimethylolethane, pentaerythritol, ditrimethylolpropane,dipentaerythritol, sorbitol, mannitol, and the corresponding alkoxylatedalcohols, especially ethoxylated and/or propoxylated alcohols.

The alkoxylation products are obtainable conventionally by reacting theabove alcohols with alkylene oxides, especially ethylene oxide orpropylene oxide. The degree of alkoxylation per hydroxyl group ispreferably from 0 to 10; that is, 1 mol of hydroxyl group can bealkoxylated with up to 10 mol of alkylene oxides.

Other (meth)acrylate compounds include polyester (meth)acrylates, whichare the (meth)acrylic esters or vinyl ethers of polyesterols, and alsourethane, epoxy or melamine (meth)acrylates.

Urethane (meth)acrylates are obtainable for example by reactingpolyisocyanates with hydroxyalkyl (meth)acrylates and, whereappropriate, chain extenders such as diols, polyols, diamines,polyamines or dithiols or polythiols.

The urethane (meth)acrylates preferably have a number-average molarweight M_(n) of from 500 to 20 000, in particular from 750 to 10 000 andwith particular preference from 750 to 3000 g/mol (as determined by gelpermeation chromatography using polystyrene standards).

The urethane (meth)acrylates preferably contain from 1 to 5, morepreferably from 2 to 4, mol of (meth)acrylic groups per 1000 g ofurethane (meth)acrylate.

Epoxy (meth)acrylates are obtainable by reacting epoxides with(meth)acrylic acid. Examples of suitable epoxides include epoxidizedolefins or glycidyl ethers, e.g., bisphenol A diglycidyl ether, oraliphatic glycidyl ethers, such as butanediol diglycidyl ether.

Melamine (meth)acrylates are obtainable by reacting melamine with(meth)acrylic acid or the esters thereof.

The epoxy (meth)acrylates and melamine (meth)acrylates preferably have anumber-average molar weight M_(n) of from 500 to 20 000, more preferablyfrom 750 to 10 000 g/mol and very preferably from 750 to 3000 g/mol; theamount of (meth)acrylic groups is preferably from 1 to 5, morepreferably from 2 to 4, per 1000 g of epoxy (meth)acrylate or melamine(meth)acrylate (as determined by gel permeation chromatography usingpolystyrene standards and tetrahydrofuran eluent).

Also suitable are carbonate (meth)acrylates containing on averagepreferably from 1 to 5, in particular from 2 to 4, very preferably 2 or3 (meth)acrylic groups, and especially 2 (meth)acrylic groups.

The number-average molecular weight M_(n) of the carbonate(meth)acrylates is preferably less than 3000 g/mol, more preferably lessthan 1500 g/mol, very preferably less than 800 g/mol (as determined bygel permeation chromatography with polystyrene standards andtetrahyrofuran solvent).

The carbonate (meth)acrylates are obtainable in a simple way bytransesterification of carbonic esters with polyhydric, preferablydihydric, alcohols (diols, e.g., hexanediol) and subsequentesterification of the free OH groups with (meth)acrylic acid or elsetransesterification with (meth)acrylic esters, as described for examplein EP-A 92 269. They are also obtainable by reacting phosgene, ureaderivatives with polyhydric, e.g., dihydric, alcohols.

Suitable reactive diluents (compounds (H)) include radiation-curable,free-radically or cationically polymerizable compounds containing onlyone ethylenically unsaturated copolymerizable group.

Examples that may be mentioned include C₁–C₂₀ alkyl (meth)acrylates,vinylaromatics having up to 20 carbon atoms, vinyl esters of carboxylicacids containing up to 20 carbon atoms, ethylenically unsaturatednitriles, vinyl ethers of alcohols containing 1 to 10 carbon atoms,α,β-unsaturated carboxylic acids and their anhydrides, and aliphatichydrocarbons having 2 to 8 carbon atoms and 1 or 2 double bonds.

Preferred alkyl (meth)acrylates are those with a C₁–C₁₀ alkyl radical,such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethylacrylate, and 2-ethylhexyl acrylate.

Mixtures of the alkyl (meth)acrylates in particular are also suitable.

Vinyl esters of carboxylic acids having 1 to 20 carbon atoms are, forexample, vinyl laurate, vinyl stearate, vinyl propionate, and vinylacetate.

α,β-Unsaturated carboxylic acids and their anhydrides may for example beacrylic acid, methacrylic acid, fumaric acid, crotonic acid, itaconicacid, maleic acid or maleic anhydride, preferably acrylic acid.

Examples of suitable vinylaromatic compounds include vinyltoluene,α-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene, and styrene, thelatter being preferred.

Examples of nitriles are acrylonitrile and methacrylonitrile.

Suitable vinyl ethers include for example vinyl methyl ether, vinylisobutyl ether, vinyl hexyl ether, and vinyl octyl ether.

Nonaromatic hydrocarbons having 2 to 8 carbons and one or two olefinicdouble bonds include butadiene, isoprene, and also ethylene, propylene,and isobutylene.

It is additionally possible to use N-vinylformamide, N-vinylpyrrolidone,and N-vinylcaprolactam.

As photoinitiators (I) it is possible to use the photoinitiators knownto the skilled worker, examples being those specified in “Advances inPolymer Science”, Volume 14, Springer Berlin 1974 or in K. K. Dietliker,Chemistry and Technology of UV- and EB-Formulation for Coatings, Inksand Paints, Volume 3; Photoinitiators for Free Radical and CationicPolymerization, P. K. T. Oldring (Eds), SITA Technology Ltd, London.

Suitable photoinitiators include, for example, monoacyl- orbisacylphosphine oxides Irgacure 819(bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide), as described forexample in EP-A 7 508, EP-A 57 474, DE-A 196 18 720, EP-A 495 751 orEP-A 615 980, an example being 2,4,6-trimethylbenzoyldiphenylphosphineoxide (Lucirin® TPO) or ethyl 2,4,6-trimethylbenzoyl-phenylphosphinate,benzophenones, hydroxyacetophenones, phenylglyoxylic acid and itsderivatives, or mixtures of these photoinitiators. Examples that may bementioned include benzophenone, acetophenone, acetonaphthoquinone,methyl ethyl ketone, valerophenone, hexanophenone,α-phenylbutyrophenone, p-morpholinopropiophenone, dibenzosuberone,4-morpholinobenzophenone, 4-morpholinodeoxybenzoin, p-diacetylbenzene,4-aminobenzo-phenone, 4′-methoxyacetophenone, β-methylanthraquinone,tert-butylanthraquinone, anthraquinonecarboxylic esters, benzaldehyde,α-tetralone, 9-acetylphenanthrene, 2-acetylphenanthrene,10-thioxanthenone, 3-acetylphenanthrene, 3-acetylindole, 9-fluorenone,1-indanone, 1,3,4-triacetylbenzene, thioxanthen-9-one, xanthen-9-one,2,4-dimethyl-thioxanthone, 2,4-diethylthioxanthone,2,4-di-iso-propylthioxanthone, 2,4-dichlorothioxanthone, benzoin,benzoin isobutyl ether, chloroxanthenone, benzoin tetrahydropyranylether, benzoin methyl ether, benzoin ethyl ether, benzoin butyl ether,benzoin isopropyl ether, 7H-benzoin methyl ether,benz[de]anthracen-7-one,1-naphthaldehyde,4,4′-bis(dimethylamino)benzophenone, 4-phenylbenzophenone,4-chlorobenzophenone, Michler's ketone, 1-acetonaphthone,2-acetonaphthone, 1-benzoylcyclohexan-1-ol,2-hydroxy-2,2-dimethylacetophenone, 2,2-di-methoxy-2-phenylacetophenone,2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone,1-hydroxyacetophenone, acetophenone dimethyl ketal,o-methoxybenzophenone, triphenylphosphine, tri-o-tolylphosphine,benz[a]anthracene-7,12-dione, 2,2-diethoxyacetophenone, benzil ketals,such as benzil dimethyl ketal,2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one,anthraquinones such as 2-methylanthraquinone, 2-ethylanthraquinone,2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amylanthraquinone,and 2,3-butanedione.

Also suitable are non-yellowing or low-yellowing photoinitiators of thephenylglyoxalic ester type, as described in DE-A 198 26 712, DE-A 199 13353 or WO 98/33761.

Of the photoinitiators stated preference is given to phosphine oxides,α-hydroxy ketones, and benzophenones.

In particular it is also possible to use mixtures of differentphotoinitiators.

The photoinitiators can be used alone or in combination with aphotopolymerization promoter, of the benzoic acid type, amine type or asimilar type, for example.

As further typical coatings additives (J) it is possible for example touse antioxidants, oxidation inhibitors, stabilizers, activators(accelerators), fillers, pigments, dyes, devolatilizers, gloss agents,antistatic agents, flame retardants, thickeners, thixotropic agents,leveling assistants, binders, antifoams, fragrances, surface-activeagents, viscosity modifiers, plasticizers, plastificators, tackifyingresins (tackifiers), chelating agents or compatibilizers.

As accelerators for the thermal aftercure it is possible, for example,to use tin octoate, zinc octoate, dibutyltin laurate ordiaza[2.2.2]bicyclooctane.

Further possibilities for addition include one or more photochemicallyand/or thermally activable initiators, such as potassiumperoxodisulfate, dibenzoyl peroxide, cyclohexanone peroxide,di-tert-butyl peroxide, azobisisobutyronitrile, cyclohexylsulfonylacetyl peroxide, diisopropyl percarbonate, tert-butyl peroctoate orbenzpinacol, and also, for example, those thermally activable initiatorswhich have a half-life at 80° C. of more than 100 hours, such asdi-t-butyl peroxide, cumene hydroperoxide, dicumyl peroxide, t-butylperbenzoate, silylated pinacols, which are available commercially, forexample, under the trade name ADDID 600 from Wacker, orhydroxyl-containing amine N-oxides, such as2,2,6,6-tetramethylpiperidine-N-oxyl,4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, etc.

Further examples of suitable initiators are described in PolymerHandbook, 2nd ed., Wiley & Sons, New York.

Besides free-radically (co)polymerized (co)polymers, thickeners that aresuitable include customary organic and inorganic thickeners such ashydroxymethylcellulose or bentonites.

As chelating agents it is possible to make use for example ofethylenediamine acetic acid and its salts and also β-diketones.

Suitable fillers include silicates, examples being silicates obtainableby hydrolysis of silicon tetrachloride, such as Aerosil® from Degussa,siliceous earth, talc, aluminum silicates, magnesium silicates, calciumcarbonates, etc.

Suitable stabilizers include typical UV absorbers such as oxanilides,triazines, and benzotriazole (the latter available as Tinuvin® gradesfrom Ciba Spezialitätenchemie) and benzophenones. These can be usedalone or together with suitable free-radical scavengers, of whichexamples include sterically hindered amines such as2,2,6,6-tetramethylpiperidine, 2,6-di-tert-butylpiperidine orderivatives thereof, such asbis(2,2,6,6-tetramethyl-4-piperidyl)sebacate. Stabilizers are usednormally in amounts of from 0.1 to 5.0% by weight, based on the solidcomponents present in the formulation.

Examples of stabilizers which are additionally suitable include N-oxyls,such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl,4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl,4-acetoxy-2,2,6,6-tetramethylpiperidine-N-oxyl,2,2,6,6-tetramethylpiperidine-N-oxyl,4,4′,4″-tris-(2,2,6,6-tetramethylpiperidine-N-oxyl) phosphite or3-oxo-2,2,5,5-tetramethylpyrrolidine-N-oxyl, phenols and naphthols, suchas p-aminophenol, p-nitrosophenol, 2-tert-butylphenol,4-tert-butylphenol, 2,4-di-tert-butylphenol,2-methyl-4-tert-butylphenol, 4-methyl-2,6-tert-butylphenol(2,6-tert-butyl-p-cresol) or 4-tert-butyl-2,6-dimethylphenol, quinones,such as hydroquinone or hydroquinone monomethyl ether, for example,aromatic amines, such as N,N-diphenylamine, N-nitrosodiphenylamine,phenylenediamines, such as N,N′-dialkyl-para-phenylenediamine, in whichthe alkyl radicals can be the same or different and consist eachindependently of from 1 to 4 carbon atoms and can be straight-chain orbranched, hydroxylamines, such as N,N-diethylhydroxylamine, ureaderivatives, such as urea or thiourea, phosphorus compounds, such astriphenylphosphine, triphenyl phosphite or triethyl phosphite, or sulfurcompounds, such as diphenyl sulfide or phenothiazine, for example.

Typical compositions of radiation-curable compositions are for example

-   (F) 20–100% by weight, preferably 40–90%, more preferably 50–90%,    and especially 60–80% by weight,-   (G) 0–60% by weight, preferably 5–50%, more preferably 10–40%, and    especially 10–30% by weight,-   (H) 0–50% by weight, preferably 5–40%, more preferably 6–30%, and    especially 10–30% by weight,-   (I) 0–20% by weight, preferably 0.5–15%, more preferably 1–10%, and    especially 2–5% by weight, and-   (J) 0–50% by weight, preferably 2–40%, more preferably 3–30%, and    especially 5–20% by weight,-   with the proviso that (F), (G), (H), (I), and (J) together make 100%    by weight.

The coating of the substrates takes place in accordance with customarymethods known to the skilled worker, which involve applying at least onecoating composition to the target substrate in the desired thickness andremoving any volatile constituents of the coating composition, whereappropriate with heating. This operation can if desired be repeated oneor more times. Application to the substrate can be made in a known way,for example by spraying, troweling, knifecoating, brushing, rolling,roller coating, pouring, laminating, injection backmolding orcoextruding. The coating thickness is generally in a range from about 3to 1000 g/m² and preferably from 10 to 200 g/m².

Additionally disclosed is a method of coating substrates which involvesapplying the coating composition to the substrate and drying it whereappropriate, curing it with electron beams or UV light under anoxygen-containing atmosphere or, preferably, under inert gas, andsubjecting it to thermal treatment where appropriate at temperatures upto the level of the drying temperature and subsequently at temperaturesup to 160° C., preferably between 60 and 160° C.

The method of coating substrates can also be performed by first applyingthe coating composition and then subjecting it to thermal treatmentfirst at temperatures up to 160° C., preferably between 60 and 160° C.,and then curing it with electron beams or UV light under oxygen or,preferably, under inert gas.

Curing of the films formed on the substrate may if desired take placeexclusively by thermal means. In general, however, the coatings arecured both by exposure to high-energy radiation and thermally.

Instead of or in addition to the thermal cure, curing may also beeffected by NIR radiation, which here is a term used for electromagneticradiation in the wavelength range from 760 nm up to 2.5 μm, preferablyfrom 900 to 1500 nm.

If two or more films of the coating material are applied over oneanother, it is possible if desired to carry out a thermal, NIR and/orradiation cure after each coating operation.

Suitable radiation sources for the radiation cure include for examplelow, medium or high pressure mercury lamps and also fluorescent tubes,pulsed emitters, metal halide lamps, electronic flash installations,which allow a radiation cure without photoinitiators, or excimerradiators. Radiation curing is effected by exposure to high-energyradiation, i.e. UV radiation or daylight, preferably light in thewavelength range λ of from 200 to 700 nm, more preferably from 200 to500 nm and very preferably from 250 to 400 nm, or by irradiation withhigh-energy electrons (electron beams; 150 to 300 keV). The radiationsources used are, for example, high pressure mercury vapor lamps,lasers, pulsed lamps (flash light), halogen lamps or excimer radiators.The radiation dose normally sufficient for crosslinking in the case ofUV curing is in the range from 80 to 3000 mJ/cm².

As will be appreciated it is also possible to use two or more radiationsources for the cure, e.g., from two to four.

These sources may also each emit in different wavelength ranges.

Irradiation can be performed where appropriate in the absence of oxygen,such as under an inert gas atmosphere. Suitable inert gases includepreferably nitrogen, noble gases, carbon dioxide, or combustion gases.Irradiation may also take place with the coating composition coveredwith transparent media. Examples of transparent media are polymericfilms, glass or liquids, such as water. Particular preference is givento irradiation in the manner described in DE-A1 199 57 900.

The invention further provides a method of coating substrates whichinvolves

-   i) coating a substrate with a coating composition as described    above,-   ii) removing volatile constituents of the coating composition to    form a film, under conditions in which the photoinitiator (I)    essentially as yet does not form free radicals,-   iii) if desired, irradiating the film formed in step ii) with    high-energy radiation, the film undergoing initial cure, and then,    if desired, mechanically working the article coated with the    precured film or contacting the surface of the precured film with    another substrate,-   iv) completing the curing of the film thermally or using NIR    radiation.

Steps iv) and iii) can also be carried out in the opposite order, i.e.,the film can first be cured thermally or by NIR radiation and then usinghigh-energy radiation.

Also provided by the present invention are substrates coated with amulticoat paint system of the invention.

The thickness of such a film to be cured as described can be from 0.1 μmto several mm, preferably from 1 to 2000 μm, more preferably from 5 to1000 μm, very preferably from 10 to 500 μm, and in particular from 10 to250 μm.

With particular preference the coating compositions of the invention aresuitable as or in exterior coatings, i.e., in those applications whichare exposed to daylight, preferably on buildings or parts of buildings,interior coatings, traffic markings, coatings on vehicles and aircraft.The coatings are employed in particular as wood, paper or plasticscoatings, for woodblock flooring or furniture for example.

The examples which follow are intended to illustrate the properties ofthe invention without, however, restricting it.

EXAMPLES

Unless specified otherwise parts in this text are to be understood asmeaning parts by weight.

Example 1

A mixture of 2.5 mol (220 g) of ethylene carbonate and 2.5 mol (180 g)of n-butylamine was stirred at 100° C. for 2 h. The reaction product wasisolated by filtration to give 398 g of crude product (clear, colorlessliquid).

The conversion as determined by GC was 99%.

Example 2

A mixture of 2.5 mol (220 g) of ethylene carbonate and 2.5 mol (247 g)of aminocyclohexane was stirred at room temperature at up to 120° C. for4 h. The reaction product was isolated by filtration to give 465 g ofcrude product (clear, colorless liquid).

The conversion as determined by GC was 97%.

Example 3

16 g of a polyethyleneimine (0.2 mol of primary and secondary aminofunctions, Lupasol® FG, BASF AG) and 1 mol (88 g) of ethylene carbonatewas stirred at 60–100° C. for 3 h. The mixture was filtered while stillhot, and 23 g of crude product (yellowish solid) were obtained. A samplewas taken, its OH number determined, and analyzed by GPC. The conversionof the primary and secondary amines was more than 90%, with aweight-average molar weight M_(w) that had increased by about 650 g/molon the starting product.

Example 4

A mixture of 0.5 mol (80 g) of the reaction mixture from example 1, 1.0mol (86 g) of methyl acrylate and 2 g of Novozym 435 (lipase fromCandida antarctica B) was stirred at 60° C. for 24 h. The enzyme wasremoved by filtration, methanol was removed in a rotary evaporator underreduced pressure and 86 g of crude product (clear, colorless liquid)were obtained.

The product is soluble in customary polyether, polyester, and urethaneacrylates and can be admixed without clouding occurring.

A sample was taken, silylated, and analyzed by GC. The reaction mixturefrom example 1 had been converted to an extent of >97%.

Example 5

A mixture of 18.7 g (0.1 mol) of the reaction mixture from example 2,1.0 mol (86 g) of methyl acrylate and 2 g of Novozym 435 (lipase fromCandida antarctica B) was stirred at RT for 24 h. The enzyme was removedby filtration, methanol was removed in a rotary evaporator under reducedpressure, and 26 g of crude product (clear, colorless liquid) wereobtained.

A sample was taken, silylated, and analyzed by GC. The reaction mixturefrom example 2 had undergone conversion to an extent of >95%.

Example 6

A mixture of 0.1 mol (OH equivalent, 7 g) of the reaction mixture fromexample 3, 1.0 mol (86.1 g) of methyl acrylate and 2.0 g of Novozym 435(lipase from Candida antarctica B) was stirred at 60° C. for 24 h. Theenzyme was removed by filtration, methanol was removed on a rotaryevaporator under reduced pressure, and 15 g of crude product (yellowishsolid) were obtained.

A sample was taken, its OH number was determined and it was analyzed byGPC. More than 95% of the alcohol functionalities have been reacted. Theweight-average molar weight M_(w) was increased by about 490 g/mol onthe starting product.

Example 7

A mixture of 5 mmol (746 mg) of 2-hydroxyethylN-[3′-(2″-hydroxyethyl-N′-propylcarbamoyl)]-carbamate, 100 mmol (8.61 g)of methyl acrylate, 1 g of 5 Å molecular sieve and 75 mg of Novozym 435(lipase from Candida antarctica B) with 5 ml of acetone whereappropriate was stirred at the stated temperature. The enzyme wasremoved by filtration, methyl acrylate was removed on a rotaryevaporator, and 1.4 g of crude product (clear, yellowish liquid) wasobtained.

A sample was taken, silylated, and analyzed by GC. According to GCanalysis the composition of the product was as follows:

Conversion Monoacrylate Diacrylate Batch Conditions [%]a [%] [%] 1 24h/40° C., 62 84 16 no acetone 2 24 h/60° C., 90 57 43 no acetone 3 24h/60° C., 82 93 7 no molecular sieve, with acetone 4 48 h/50° C., 98 <298 no acetone aConversion to monoacrylate and diacrylate in total

Example 8

A mixture of 1.0 mol (119.1 g) of hydroxypropyl carbamate (isomermixture of 2-hydroxy-1-propyl carbamate and 3-hydroxy-2-propylcarbamate), 10.0 mol (860 g) of methyl acrylate, 172 mg of4-methoxyphenol, 43 mg of phenothiazine, 300 g of molecular sieve (5 Å)and 9.0 g of Novozym 435 (lipase from Candida antarctica B) was stirredat 60° C. for 72 h. The enzyme and molar sieve were removed byfiltration, methyl acrylate was removed on a rotary evaporator underreduced pressure, and 162 g of crude product (clear, colorless liquid)were obtained. A sample was taken and analyzed by GC-MS. Thehydroxypropyl carbamate had reacted to an extent of 96%.

Example 9

A mixture of 5 mmol (525 mg) of 2-hydroxyethyl carbamate, 25–100 mmol ofmethyl acrylate, 1.0 g of molecular sieve (5 Å) and 30 mg of Novozym 435(lipase from Candida antarctica B) was stirred at 60° C. for 8 h in theabsence of a polymerization inhibitor. A sample was taken and analyzedby GC. The conversions of the 2-hydroxyethyl carbamate are described inthe table below. The product is obtained in the form of colorlesscrystals.

Conversion [%] Conversion [%] Methyl acrylate with molecular sievewithout molecular sieve  50 mmol 85 80 100 mmol 99 89

Example 10

52.5 g of hydroxyethyl carbamate were admixed with an excess of methylacrylate (129 g) and with 0.6 g of Fascat® 4201 E-Coat (dibutyltinoxide, Elf Atochem) and stabilizers (0.5 g of MEHQ and 0.5 g of BHT(butylated hydroxytoluene)).

Initially the mixture was stirred for 2 hours at 80° C.; the thin-layerchromatogram showed only a very low conversion. Then 18 g of molecularsieve were added. The reaction temperature was held between 90° C. and110° C. and stirring was continued for 24 h. The molecular sieve wasremoved by filtration and then the excess methyl acrylate was distilledoff. This gave a clear, yellow liquid which after one day began partlyto crystallize.

The yield of mixture was (according to NMR) approximately 80%. A sampleof the mixture was taken and was analyzed by GC-MS. In addition to thedesired product (about 40% of the mixture) a series of byproducts werein evidence (e.g., glycol and acrylated glycol derivatives).

Comparative Example

A mixture of 3 mmol (1.49 g) of 2-hydroxyethylN-[3′-(2″-hydroxyethyl-N′-propylcarbamoyl)]-carbamate, 60 mmol (5.16 g)of methyl acrylate, 0.04 g of p-toluenesulfonic acid (TSA) and 500 ppmof hydroquinone monomethyl ether for stabilization was heated to boilingunder reflux. Thereafter an azeotrope of methanol and methyl acrylatewas removed by distillation. After about 24 hours of reaction themixture is cooled and the acrylated carbamate is obtained by vacuumdistillation in a yield of 81%.

Conversion Monoacrylate Diacrylate Conditions [%]a [%] [%] 24h/comparative 81 61 12 example with p-TSS aConversion to monoacrylateand diacrylate in totalCoating System

The coating composition from example 7 (batch 4) was mixed with 4% byweight of Irgacure® 500 photoinitiator from Ciba Specialty Chemicals.

The mixture obtained was applied to a system consisting of cationicdipcoating, surfacer, and a basecoat (brilliant black) from BASFCoatings AG, Münster. The basecoat was predried at 80° C. for 10 minutesand exposed five times under an undoped high-pressure mercury lamp(output 120 W/cm) with a lamp-to-substrate distance of 12 cm and beltspeed of 5 m/min.

The film thickness after exposure was about 50 μm.

The pendulum damping was determined in accordance with DIN 53157 and isa measure of the hardness of the coating. The result is stated inpendulum swings for a 50 μm film. High figures in this test denote highhardness.

The Erichsen cupping was determined in accordance with DIN 53156 and isa measure of the flexibility and elasticity. It is reported inmillimeters (mm). High figures denote high flexibility. The adhesionwith crosshatching was determined in accordance with DIN 53151 andreported as ratings. Low figures denote high adhesion.

TABLE 1 Coating 1 Coating 2 Amine- Polyester acrylate modified polyetherLaromer ® PE55W acrylate Laromer ® without/with 20% PO 84F without/withby weight coating 20% by weight composition from coating composition ex.7, batch 4 from ex. 7, batch 4 Exposure [mJ/cm2] 1900 1900 Filmthickness 55 60 [μm] Pendulum hardness 32/40 45/50 [sec] Erichsencupping 6.3/5.5 4.6/5.0 after curing [mm] Adhesion with 5/4–5 5/4–5crosshatching/ adhesive tape removal

TABLE 2 (Use of liquid products as reactive diluents) Coating 3 80%Coating 4 80% epoxy acrylate epoxy acrylate Coating 5 (comp.) 20% byweight 20% by weight 80% epoxy acrylate coating coating 20% by weightcomposition composition from hexanediol from ex. 4 ex. 7, batch 4diacrylate Exposure 1900 1900 1900 [mJ/cm2] Film thickness 55 60 50 [μm]Viscosity [Pas] 30 70 18 Pendulum 150 170 175 hardness [sec] Erichsen1.8 1.3 0.8 cupping after curing [mm] Adhesion with 5/4 5/4 5/5crosshatching/ adhesive tape removal

The epoxy acrylate used is obtainable by reacting bisphenol A diglycidylether with acrylic acid.

1. A process for preparing (meth)acrylic esters (F) comprising at leastone urethane group comprising c) reacting an alcohol (C) comprising atleast one urethane group with (meth)acrylic acid or with a saturatedalcohol (D) ester of (meth)acrylic acid.
 2. The process of claim 1,wherein the conversion in stage c) is set to at least 95%.
 3. Theprocess of claim 1, wherein the reaction c) is conducted at from 20 to80° C.
 4. The process of claim 1, wherein the alcohol (C) comprising atleast one urethane group is obtained by a) reacting an amine (A) with acarbonate (B).
 5. The process of claim 4 wherein the alcohol (C)comprising at least one urethane is obtained by a reaction comprising

wherein R³ and R⁴ independently are hydrogen, a C₁–C₁₈ alkyl, a C₂–C₁₈alkyl uninterrupted or interrupted by one or more oxygen and/or sulfuratoms and/or by one or more substituted or unsubstituted imino groups,or are a C₂–C₁₈ alkenyl, a C₆–C₁₂ aryl, a C₅–C₁₂ cycloalkyl or a five ora six-membered heterocycle comprising oxygen, nitrogen and/or sulfuratoms; and Y is a C₂–C₂₀ alkylene or a C₅–C₁₂ cycloalkylene or is aC₂–C₂₀ alkylene comprising one or more oxygen and/or sulfur atoms and/orone or more substituted or unsubstituted imino groups and/or one or morecycloalkyl, —(CO)—, —O(CO)O—, —(NH)(CO)O—, —O(CO)(NH)—, —(CO)— or—(CO)O— groups.
 6. The process of claim 1, wherein the reaction c) isconducted in the presence of an enzyme (E).
 7. The process of claim 6,wherein the enzyme (E) is a lipase, an esterase or a protease.
 8. Theprocess of claim 5, wherein R³, R⁴, or R³ and R⁴ independently are aC₂–C₁₈ alkenyl, a C₆–C₁₂ aryl, a C₅–C₁₂ cycloalkyl or a five memberedheterocycle or a six-membered heterocycle comprising oxygen, nitrogenand/or sulfur atoms, and wherein at least one of R³ and R⁴ aresubstituted by an aryl, an alkyl, an aryloxy, an alkyloxy, at least oneheteroatom, a heterocycle, a group of the formula —[X_(i)]_(k)—H, or acombination thereof; wherein k is a number from 1 to 50, and whereinX_(i), for i=1 to k, is selected from the group consisting of—CH₂—CH₂—O—, —CH₂—CH₂—N(H)—, —CH₂—CH₂—CH₂—N(H)—, —CH₂—CH(NH₂)—,—CH₂—CH(NHCHO)—, —CH₂—CH(CH₃)—O—, —CH(CH₃)—CH₂—O—, —CH₂—C(CH₃)₂—O—,—C(CH₃)₂—CH₂—O—, —CH₂—CH₂—CH₂—O—, —CH₂—CH₂—CH₂—CH₂—O—, —CH₂—CHVin-O—,—CHVin-CH₂—O—, —CH₂—CHPh—O—, and —CHPh—CH₂—O—, wherein Ph stands forphenyl and Vin stands for vinyl.
 9. The process of claim 5, wherein theradical Y is substituted by an aryl, an alkyl, an aryloxy, an alkyloxy,at least one heteroatom, a heterocycle, or a combination thereof. 10.The process of claim 6, further comprising separating the enzyme fromthe reaction mixture in c) by filtration, absorption, centrifugation ordecanting.
 11. The process of claim 6, further comprising separating anorganic solvent from the reaction mixture in c) by distillation,rectification, filtration or chromatography.
 12. The process of claim 5wherein (A) is polyethyleneimine, a hydrogenated polyacrylonitrile, astraight chain, a branched chain or a dendritic polymer having aminofunctions or an at least partly hydrolyzed poly-N-vinylformamide havinga weight-average molecular weight Mw of from 200 to 1 000 000.